1. Field of the Invention
This invention relates to a copying apparatus having a magnification changing function, and more particularly to a copying apparatus provided with an optical adjusting mechanism capable of simply compensating for any error of the focal length in the manufacture of a projection lens system.
2. Description of the Prior Art
Generally, the following errors occur as manufacturing errors in a copying apparatus or the like:
(1) An error from the initial design value of the focal length of the projection lens system; and PA1 (2) An error from the initial design value of the object-image distance. These errors may result in an incorrect focus which in turn may result in degradation of the quality of copy image, and such errors must be corrected and particularly must be corrected at each magnification in a variable magnification copying apparatus.
If a so-called zoom lens is used as the lens, the object-image distance becomes constant at each magnification.
Generally, in a copying apparatus, one-to-one magnification becomes the standard, but in a variable magnification copying apparatus using a zoom lens, an error from the initial design value of the object-image distance may be compensated for during one-to-one copying. At this time, the focal length of the lens is varied and the manufacturing error of the lens itself must also be compensated for.
In a copying apparatus using a single focus lens as the projection lens system, where the single focus lens is deviated from a predetermined focal length due to the manufacturing error, a method of correcting the focal length thereof is known from Japanese Laid Open Patent Application No. 24832/1978. According to this, a load is imparted to a mirror disposed in the lens to create a deformation in the elasticity range and the focal length is adjusted by the curvature of this mirror. With this method, however, the deviation of the lens system from its initial performance has been great.